1. Technical Field
The technology relates to methods and structures for increasing current flow in strained semiconductor material.
2. Discussion of the Related Art
Transistors are fundamental device elements of modem digital processors and memory devices, and have found numerous applications in various areas of electronics including data processing, data storage, and high-power applications. Currently, there are a variety of transistor types and designs that may be used for different applications. Various transistor types include, for example, bipolar junction transistors (BJT), junction field-effect transistors (JFET), metal-oxide-semiconductor field-effect transistors (MOSFET), vertical channel or trench field-effect transistors, and superjunction or multi-drain transistors.
Two types of transistors have emerged within the MOSFET family of transistors that show promise for scaling to ultra-high density and nanometer-scale channel lengths. One of these transistor types is a so-called fin field-effect transistor or “finFET.” The channel of a finFET is formed as a three-dimensional fin that may extend from a surface of a substrate. FinFETs have favorable electrostatic properties for complementary MOS (CMOS) scaling to smaller sizes. Because the fin is a three-dimensional structure, the transistor's channel can be formed on three surfaces of the fin, so that the finFET can exhibit a high current switching capability for a given surface area occupied on substrate. Since the channel and device can be raised from the substrate surface, there can be reduced electric field coupling between adjacent devices as compared to conventional planar MOSFETs.
The second type of transistor is called a fully-depleted, silicon-on-insulator or “FD-SOI” FET. The channel, source, and drain of an FD-SOI FET is formed in a thin planar semiconductor layer that overlies a thin insulator. Because the semiconductor layer and the underlying insulator are thin, the bulk region of the transistor (that lies below the thin insulator and is sometimes referred to as a “back body” region) can act as a second backside gate for the thin body in the thin semiconductor layer. The thin layer of semiconductor on insulator permits higher body biasing voltages that can either boost performance or reduce leakage current depending on the desired operating mode. The thin insulator also reduces leakage current to a transistor's body region that would otherwise occur in bulk FET devices.